Pulse or digital communications – Spread spectrum
Reexamination Certificate
1997-02-19
2001-09-11
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
C375S132000, C375S139000, C375S140000, C375S267000, C455S134000
Reexamination Certificate
active
06289036
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to spread spectrum communication apparatus and method for receiving a wide-band spread spectrum signal.
FIG. 2
shows a spread spectrum communication apparatus.
A received spread signal is supplied from one of antennas
111
and
112
which is selected by an antenna switch
110
, to a low-noise amplifier
113
via a band-pass filter (BPF)
109
. Then, a frequency of the received signal is converted into a predetermined frequency by a frequency converter
114
to which a local oscillator
102
is connected. The received signal which has been subjected to the frequency conversion is further subjected to predetermined band restriction by a band-pass filter (BPF)
115
, and is then supplied to a variable amplifier
116
. After then, the received signal of which level has been set at a predetermined reception level is supplied to a demodulator
117
to be demodulated to data S
3
, and the data S
3
is subsequently supplied to a control unit
118
.
In this case, an output from the variable amplifier
116
is also supplied to a wave detector
119
to detect field intensity of the received signal. A voltage detected by the wave detector
119
is applied to an automatic gain control (AGC) voltage generator
120
, such that the applied voltage acts as a control voltage of the variable amplifier
116
to set the level of the received signal as a predetermined signal level. Also, an output from the AGC voltage generator
120
is supplied to an antenna switch signal generator
121
to switch or change the antenna in accordance with a signal S
7
in a case where a level of such output is equal to or smaller than a predetermined threshold level.
However, in the spread spectrum communication apparatus shown in
FIG. 2
, since wave detection is performed by the wave detector
119
for an entire band (i.e., a band of the BPF
115
) of the received signal, if there are noise components, e.g., an unnecessary wave included in the band, a cross modulation wave generated in a system, and the like, voltage levels of these noise components are also detected, whereby it is difficult to detect a normal signal level. Especially, as the level of the received signal becomes lower, an amplification factor of the variable amplifier
116
becomes larger, whereby only noise power is further amplified. Therefore, the level of the received signal can not be accurately detected. As a result, it is difficult to switch the antenna normally.
Further, since the received signal is a wide-band spread signal, a fall of spectrum within the band has various forms because of multipath. In this case, the multipath represents a phenomenon in which there are a plurality of paths, e.g., a reception side receives a direct wave and a reflected wave or receives a plurality of reflected waves.
FIGS. 3A
to
3
C respectively show states of the fall of spectrum of the received signal because of the multipath.
FIG. 3A
shows the state that there is no fall of spectrum of the received signal because of the multipath,
FIG. 3B
shows the state that there is a fall of spectrum at a frequency adjacent to a central frequency f
0
(i.e., apart from the central frequency f
0
by f
1
), and
FIG. 3C
shows the state that there is the fall of spectrum at the central frequency f
0
. In the case of
FIGS. 3B and 3C
, in the apparatus shown in
FIG. 2
, if received power is uniform within the band, the wave detector
119
detects the same-level voltage.
However, error generation probability in the case of the fall of spectrum shown in
FIG. 3B
tends to be higher than that in case of the fall of spectrum shown in FIG.
3
C. That is, as the fall of spectrum adjacent to a main lobe of the received signal is larger, the error generation probability tends to be higher.
Therefore, in the apparatus shown in
FIG. 2
, since the received signal is subjected to the wave detection for the entire band, differences of the fall of spectrum cannot be judged. Thus, there is a drawback that the antenna is switched only based on the field intensity of the received signal.
FIG. 7
shows the structure of a conventional spread spectrum communication apparatus which relates to transmission power control.
In
FIG. 7
, a code generator
7
generates a pseudo-noise (PN) code for use in de-spreading, and a multiplier
3
multiplies a received signal by an output of a local oscillator
10
. An automatic gain control (AGC) voltage generator
19
outputs a control signal to a variable gain amplifier on a reception side. Also, the AGC voltage generator
19
outputs the control signal to a variable gain amplifier
13
on a transmission side.
In this manner, if a correlation output is used for transmission power control, there is a drawback that a long time is required.
Such drawback also occurs in a case where the correlation output is used for switching the antenna.
SUMMARY OF THE INVENTION
An object of the present invention is to improve spread spectrum communication.
Another object of the present invention is to increase reliability of the spread spectrum communication.
Another object of the present invention is to quickly and accurately select a desired antenna from among a plurality of antennas which are used for the spread spectrum communication.
Another object of the present invention is to quickly and accurately control transmission power of a spread spectrum signal, to a desired value.
The above and other objects of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.
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Saito Katsuo
Takasaki Atsushi
Canon Kabushiki Kaisha
Chin Stephen
Fitzpatrick ,Cella, Harper & Scinto
Liu Shuwang
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